Polyimides, specifically polyetherimides (PEI) are high performance polymers having high strength, heat resistance, and modulus, and broad chemical resistance. Polyetherimides are widely used in applications including automotive, telecommunications, aerospace, electrical/electronics, transportation, food service, and healthcare. There has been a significant interest in developing thermoplastic polymers that can resist burning. The use of phosphates as flame retardants for thermoplastic polymers is generally known, particularly the use of monophosphates, for example, triphenyl phosphate, tricresyl phosphate, diphenylcresyl phosphate, and the like. Such monophosphate esters tend to suffer from several drawbacks including migration to the surface during molding of the thermoplastic composition (often referred to as “juicing”). Furthermore, to achieve an acceptable level of flame retardancy, additional flame retardants are often employed in combination with the monophosphates, particularly halogen-containing flame retardants. Halogen-containing flame retardants are undesirable because of environmental concerns and pitting of the mold surface. If high concentrations of the above-mentioned phosphate esters are employed, a decrease in heat resistance and impact strength can result.
In addition to the flame retardant properties required for use in specific applications, polyetherimides meeting certain processing requirements are also of interest. For example, the melt flow rate of polyetherimide compositions is significantly lower compared to semicrystalline thermoplastic polymer composites, for example, polyphenylene sulfide, polyetheretherketone, and the like. There remain certain applications where an increased melt flow rate of polyetherimide compositions would be desirable. For example, in the rapidly developing area of portable hand-held electronic devices, there is a need for parts with very thin walls for applications including computer tablets and smart phones. Lower molecular weight polyetherimide can provide higher flow, but at the expense of other properties including impact strength. Thus there is a need for materials that will not only flow to fill such long, thin parts but will have increased modulus and strength to ensure that devices made from these parts will have sufficient rigidity to protect the electronics in the end use.
Accordingly, there remains a continuing need for improved polyetherimide thermoplastic compositions having the desired combination of improved melt flow rate and mechanical properties including improved elongation, higher strength, and higher impact, while maintaining acceptable levels of flame retardancy.